1. Field of the Invention:
This invention concerns a process for the preparation of 5-chloro-2-pentanone by ketalization of a levulinic acid ester with ethylene glycol to obtain (1) catalytic hydrogenation of (1) to obtain 3-(2-methyl-1, 3-dioxolan-2-yl)propan-1-ol (2), and reaction of this dioxolane derivative with hydrochloric acid acid to obtain 5-chloro-2-pentanone (3). ##STR1##
2. Discussion of the Background:
Syntheses of 5-chloro-2-pentanone have long been known from the literature. The most popular method is the reaction of alpha-acetyl-gamma-butyrolactone with hydrogen chloride (Org. Synth. CV4, 1963, 597). A drawback in this procedure is the use of costly alpha-acetyl-gamma-butyrolactone, which is available by ester condensation of gamma-butyrolactone, for example, and ethyl acetate in the presence of equimolar amounts of metallic sodium.
Numerous authors describe the reaction of 4-hydroxy-2-pentanone with hydrogen chloride to obtain (3), for example Ishimaru, Chem. Abstr. 1957, 17728. 5-Hydroxy-2-pentanone is also a costly chemical that makes the process uneconomical.
On the other hand, L. Willimann and H. Schinz, Helvetia Chem. Akta, 32, 1949, 2151, use inexpensive ethyl levulinate (R =C.sub.2 H.sub.5), ketalize it with ethylene glycol, and reduce (1) with a large excess of metallic sodium and ethanol to obtain (2). The generally high chlorine content of the levulinic ester derived from its preparation does not interfere with this method of hydrogenation of the ketal. A drawback in this procedure is the use of costly metallic sodium that can be handled only with caution, and the disposal of the waste products formed from it.
All known processes for preparing 5-chloro-2-pentanone either start with costly starting materials or use expensive chemicals in large amounts during the synthesis whose disposal involves environmental protection problems. A process by which the ketal of a levulinic ester (1) be hydrogenated catalytically under ordinary conditions to obtain (2) is desirable.
The reaction of (2) with hydrochloric acid to obtain (3) should present no problems, since according to Willimann and Schinz, 5-hydroxy-2 pentanone can be prepared from (2) by reaction with water and a small amount of acid, and its reaction with hydrochloric acid to obtain 5-chloro-2-pentanone (3), as mentioned above, is likewise described in the literature.
The problem, therefore, is to develop a process by which 3-(2-methyl-1,3-dioxolan-2-yl)propan-1-ol (2) can be prepared at low technical cost and without using expensive reagents, from which 5-chloro-2-pentanone is obtained by reaction with hydrochloric acid. 5-Chloro2-pentanone has great economic importance as a pharmaceutical raw material and as the starting material for the production of cyclopropyl methyl ketone.
When the ketal of a levulinic ester (1) is hydrogenated catalytically by the customary methods of ester hydrogenation, for example with a commercial copper chromite catalyst, 1, 4-pentanediol is obtained, i.e., the dioxolane ring is opened by hydrogenolysis. A need continues to exist, therefore, for a new and economical method for preparing 5-chloro-2-pentanone.